The present invention relates to a metallizable, sealable, biaxially stretch-oriented multi-ply film comprising a base layer essentially of polypropylene, a first polyolefinic facing layer and a second polyolefinic facing layer, all the layers containing a neutralizing agent and a stabilizer against thermal degradation.
Composite films or laminates which can be metallized are already known from the state of the art. Thus, for example, EP-A 122,495 discloses a film laminate having a surface roughness Ra from 0.2 to 1.5 .mu.m and comprising an oriented polypropylene film and a layer laminated thereto, which is composed of an ethylene/propylene copolymer, this layer containing 10 to 50% by weight of the ethylene component. A metal layer can be laminated to both layers. The laminate is said to show excellent adhesive strength on metal layers, at least in comparison with paper layers, and to exhibit good gloss and transparency. Either of the two layers can generally contain conventional additives, such as heat stabilizers, antioxidants, antistatic agents, fillers and brighteners.
Moreover, EP-A 21,672 describes a laminate which is produced by co-extrusion and comprises an inner layer of a propylene homopolymer and at least one outer layer of an ethylene/propylene copolymer which does not contain any added lubricants. The laminate is corona-treated in order to improve the adhesion of a metal layer applied to the outer layer(s). If an outer layer is not metallized, it is sealable. Due to the absence of lubricants from at least one of the outer, non-metallized layers, however, the laminate may not easily run in the machine and, owing to the composition of the outer layers, will also not show a uniform corona treatment-effect promoting adhesion of the metal layer.
As shown by the discussion of the state of the art, none of the documents has hitherto been directed to an optimization with respect to the sealing properties, the metal adhesion or even the metal gloss of the metal layer applied to the particular laminate.